Production of butadiene



Aug M 3945- F. E. FREY PRODUCTION OF BUTADIENE Original Filed March 13,1941 INVENTOR Patented Aug. 14, 1945 PRODUCTION oF BUTADIENE FrederickE. Frey, Bartlesville, okla., assignor to Phillips Petroleum Company, acorporation of Delaware Original application March 13, 1941, Serial No.383,235. Divided and this application April 23, 1942, lSerial No.440,213

3 Claims.

This invention relates to the concentration of diolen hydrocarbons. Itrelates further to the concentration of low boiling diolens, moreparticularly butadiene, from mixtures containing other hydrocarbons ofclosely adjacent boiling points. As one modification, it relates to theproduction of a normal C4 hydrocarbon mixture by the dehydrogenation ofnormal butane and the separation of a butadiene concentrate therefrom.This application is a division of my copending application Serial No.383,235, filed March 13, 1941, and also is a continuation-in-part of mycopending application Serial No. 354,890, filed August 30, 1940. Y

Diolens are produced in a number of ways which include cracking ofheavier oils, pyrolysis of gaseous hydrocarbons. other than methane, thecopolymerization of acetylene and ethylene to fol-ln butadiene,catalytic and thermal conversion of alcohols, both of the same number ofcarbon atoms per molecule as the desired diolefin and of a fewer numberof carbonv atoms per molecule, and other more or less involved chemicalprocesses, as well as the dehydrogenation of the corresponding olenswhich in turn may have been produced by the dehydrogenation of thecorresponding parailins. Although this latter procedure is one of themore direct ways of producing diolefins it has not yet found veryextensive commercial application, and one'of the obstacles in itscommercial developmentl has been the difculty of effecting separation ofolens and diolelfins from each other and from mixtures containing thecorresponding parains.

In my aforementioned copending vapplication 1 of which this is gtcontinuation-impart, I have disclosed a process of producing low boilingdioleflns from the corresponding parafins in which a singledehydrogenation step is employed. As discussed therein, thisdehydrogenation step apparently does not form the major part of thediolen product by a dehydrogenation of a parain directly to a diolefinwith no intermediate reactions, but apparently cooperates with the restof the process to effect a dehydrogenation of parains other products andare returned to the dehydrogenation along with fresh parain hydrocarbonmaterial.

I have now found that eflicient separation of butadiene from a C4fraction of the eiiluent of such a dehydrogenation process can bereadily carried out, and the butadiene recovered in a state of highpurity, by a series of fractional distillation steps, in the firstof'which. sulfur dioxide is present in. a limited amount, and in thesecond of which essentially no sulfur dioxide is presen-t. While myseparation step is quite advantageously combined with a step for thedehydrogenation of normal butane to produce butadiene such as isdisclosed in my copending application, it is understood that in 'itsbroadest modification my separation step can operate on any Ci fractionwhich contains butadiene and other C4 hydrocarbons which are diflicultto remove therefrom.

It has been disclosed in U. S. 2,186,524, of which I am a coinventor,that sulfur dioxide forms minimum-boiling azeotropic mixtures with eachof the butanes and butenes. I have .now found that if a C4 fractioncontaining butadiene together with normal butane and normal butanes isfractionally distilled in the presence of sulfur dioxide, the amount ofsulfur dioxide can be so limited that the overhead fraction containssubstantially l all the normal butane, l-butene and sulfur dioxidecharged to the distillation. the kettle product will thencontain4,2V-butenes. and substantially all the butadiene charged to theprocess, and butadiene can be separated in a state of high concentrationfrom this kettle product by subsequent fractional distillation in theabsence of sulfur dioxide. In the presence of actinic light and ofcertain catalysts butenes and butadiene form sulfones and/orheteropolymeric compounds of extremely high molecular weight. Suchreactionsy are not desirable in connection with my process, and are tobe avoided.

It is an object of my invention to4 produce low boiling diolens in highconcentration.

Another object of my invention is to obtain a butadiene fraction of highconcentration from the dehydrogenation of normal butane.

Further objects and advantages of my invention will become apparent fromthe accompanying disclosure and discussion.

`My invention will now be more specifically described in connection withthe accompanying drawing which shows diagrammatically by Way of a flowsheet an arrangement of apparatus for practicing one modication of myinvention. In

this modification the invention will be described I in connection with adehydrogenation step for producing butadiene from normal butane.

Referring now to the drawing, a paraffin hydronormal butenes which willbe passed to the pipe I through pipes 51 and/or 85. The dehydrogenationis conducted to effect a dehydrogenation both of normal butane andnormal butenes to form butenes and butadiene respectively, along withfree hydrogen. When a steady state of operation is reached only alimited amount of dehydrogenation per pass will actually take place,since the net reaction will be the dehydrogenation of a small amount ofbutanevto form butenes` and of butenesto form a corresponding amount ofbutadiene, and a large substantially adiabatic catalyst chamber may beused with adequate heating of the stream charged to such chamber. Theresultant products pass .through pipe I3 and valve I4 to the separatingmeans I5. In separating means I5, lCa and lighter material includingfree hydrogen is separated from the C4 hydrocarbons and removed throughpipe I8 and valve I'I. If any C and heavier material is present in theeluent of the dehydrogenation, this material should also be removed, as'through pipe I8 'and valveIS." H

A resulting C4 hydrocarbon fraction is passed from separating means I5through pipe 20 and may be passed through valve 2| to an absorption unit22. The absorption unit 22 is used to eect a preliminary concentrationlof butenes and butadiene, which may be d one by using any suitableabsorption-operation, 'but'which is more advantageously accomplished incombination with the present invention by using a liquid sulfur dioxideas a selective absorbent. In such a caseif desired, it may constitutethe sole hydrocarbon material charged to the process. If the absorptionunit 22 is employed as Just discussed, such a C4 fraction may be passedthrough pipe 25 and valve 35 to pipe 20. However, if it is not desiredto use such an absorption means for concentrating the unsaturatedhydrocarbons, the C4 iraction may be passed from pipe 23 through pipe l1and valve 38 to pipe 3l and on to the fraction 'distillation unit 40. Inmany instances' when the dehydrogenation unit l2 is used to produce allor part of the butadiene, it will not be necessary 'to use theabsorption unit 22 and the C4 fracis removed through pipe 22 and may bedischarged from the system through pipe 23 and valve 2li or, ii desired,may be passed through valve 29 to pipe 5l for recycle within the system,as will be discussed hereinafter.

In the absorption unit 22; liquid sulfur dioxide selectively dissolvesnormal butenes land butadiene and will also take up a certain amountl ofnormal butane. The rich absorption liquid is passed through pipe lBlandvalve 32 to a irac-l tional distillation unit &0.

When a normal C4 ractionfis available from any suitable source, such asa fraction obtained from the gases resulting from the cracking ofheavier oils or in the cracking o1" light gases to form normally gaseousoleiins, such a material may be charged to the process through pipe 33and valve 34 and may join a C4 fraction passing from the separating unitI5 through pipe 20 or,

tion from separating means I5 may be passed directly through pipe 20,pipe 35 and pipe 31 to pipe 3l and the fractional distillation unit 40,as

' will be readily appreciated.

In'fractional distillation unit 40, which is illustrateddiagrammatically as a single fractionating column. a distillation of theC4 hydrocarbons takes place in the presence of sulfur dioxide, which isadded in amount suflicient to form azeotropic mixtures withsubstantially all of the normal butane and l-butene fraction and in anamount so limited that little if any of the 2- butenes or butadiene areincluded. Sulfur dioxide for this purpose may either enter thedistillation column along with the hydrocarbons through pipe 3| fromabsorption unit 22, or may be introduced separately at one or more otherpoints along the line of the distillation column through pipe 42 andvalve 43 and/or at some other part of the column as through pipe 48 andvalve 49. When it is desired to add sulfur dioxide to the materialpassing through pipe 3i this may be accomplished. by suitable control ofvalve 4I in pipe 25.

A low boiling mixture containing sulfur dioxide, normal butane andl-butene is passed from the top of the fractionating column 40 throughpipe 45, cooling and condensing coil 46 and valve 4l to a suitableseparating means such as separator 50. In this separating means asuitable separation may be effected between sulfur dioxide andhydrocarbon constituents passing with it through pipe 45. vThis may beaccomplished by suitable condensation and subatmospheric cooling totemperatures within the range of about +20 to 100 F., or by a furtherazeotropic distillation such as is disclosed rin U. S. Patent 2,186,524,or by other suitable operations. A sulfur dioxide-rich material ispassed from separator 50 through pipe 5I and may be discharged from theprocess entirely or in part through valve 52. Generally, however, asubstantial portion thereof will be returned to the fractionating column60 through pipe 53 and valve 54 as a liquid reflux. If the olen contentof this stream tends to build up too high a value, such material may beremoved through valve S52 for a further vseparation of more or less puresuliui dioxide which may be reintroduced in the system through pipeHydrocarbon material separated from 'sulfur dioxide in separator 50 maybe removed through pipe 55 and may be passed entirely or in part fromthe system through valve 56. However, when dehydrogenation unit I2 is vapart of the process, it will generally be desirableto recycle all or apart of the hydrocarbons contained in this material to thisdehydrogenatiori, and this may be effected by passing any desiredVportion of the stream from pipe 5.5 through pipe 51 and through valve 58to pipe I Il. If this stream contains an appreciable proportion o!sulfur dioxide, this should be removed 'before the material is passed tothe dehydrogenation unit. Such removal may if desired be effected bypassing the stream through pipe and valve 6| to a scrubber 62 andpassing purified hydrocarbons from the scrubber 62 rthrough pipe 61 andvalve 68 back to pipe 51 with valve 58 being closed. A suitablescrubbing agent such as water or an alkali solution such as sodiumhydroxide or sodium carbonate may be passed to the scrubber through pipe63 and valve 64 to effect the removal of sulfur dioxide from thehydrocarbons treated therein and the contaminated scrubbing medium maybe removed through pipe and valve 66 for regeneration or such othertreatment as may seem desirable. Other suitable means for separatinghydrocarbons from -sulfur dioxide may be used, as may seem desirable orexpedient.

From the bottom of fractional distillation means 4U a kettle product,which will comprise essentially Z-butenes and butadiene and which shouldbe substantially free of sulfur dioxide, is passed through pipe 10 andvalve 1I to a second fractional distillation means 12. If there issufficient sulfur dioxide in this material to require its removal, thismay be accomplished by passing the stream from pipe 10 through pipe 13and valve 14 for suitable purification as by treatment with a suitablescrubbing medium in'scrubber- 15. A suitable scrubbing medium may beadded through pipe and valve 92, and the spent scrubbing medium may beremoved from the system through pipe 18 and valve 19. 'I'he purifiedhydrocarbon material is passed through pipe 16 and valve 11 back to pipe10 and fractional distillation means 12, valve 1| being closed.

The fractional distillation unit 12 is so operated as to effect aseparation of a substantially pure butadiene fraction, which shouldgenerally contain more than per cent butadiene and preferably more thanper cent butadiene, although a purity greater than about 98 per centwill generally not be necessary. This fraction is removed as an overheadproduct through pipe 8| and valve B2 for whatever subsequent use may bedesired. The kettle product, which will contain substantial quantitiesof Z-butenes, is removed through pipe 83 and may be discharged from thesystem through valve 64. In one modification of my process it may bedesirable to pass a portion of this kettle 'product back to thefractional distillation unit 46, and this may be accomplished by passingthe desired portion through pipe 85,

` pipe 81 and valve 88 to a point in the upper portion of the fractionaldistillation unit 40, or as may be found more desirable in someparticular instance, it may be passed from pipe 81 through pipe 89 andvalve 90 to a point in the lower part of this fractional distillationunit. When the dehydrogenation unit I2 is a part of my process and thiskettle product does not contain too high a concentration of butadiene, aportion of it may be passed through valve 86 in a continuation of pipe85 t0 pipe IU.

While fractional distillation units 40 and 12 have been shown as singleunits, itis to be understood that this is merely diagrammatic and eitherone or both of them may comprise two or more fractional distillationcolumns, each with suitable bubble trays or packing not shown, to affordintimate contact by the reflux liquid and ascending vapors with suitableheating means for the kettle, and cooling means for the top, refluxaccumulators and refiux lines and the like as will be readily understoodby one skilled in the art. It

will be'desrable that the butadiene-containing material, especially whenthe butadiene is in a somewhat concentrated state, should not be heatedto too high a temperature since this material polymerizes somewhatreadily. It is well known that sulfur dioxide forms sulfones and highmolecular weight heteropolymeric compounds with butenes and butadiene.Such chemical reactions take place in the presence of actinic light andalso in the presence of certain catalysts and are to be avoided. In someinstances it may be necessary to add materials to inhibit the formationof such compounds, such as phenylbeta-naphthylamine, pyrogallic acid,hydroquinone, catechol, resorcinol, cresols and similar phenoliccompounds. Any iso-C4 hydrocarbons presentl in the charge tofractionating means 40 will be removed therefrom in the overheadproduct, and may be discharged from the system through valves 52`and/or56. Some or all of any iso-Gis present in the material charged toseparating means I5 may be removed, as a part of the Ca and lightermaterial, through pipe I6.

Although it is desirable that the major part of the 2-butenes beseparated along with the butadiene as a kettle product, at times abetter separatioi can be effected if la small portion of the Z-butenes,especially the trans-isomer, is permitted to pass from the distillationcolumn 40 through pipe 45 as a part of the overhead product. As anexample of my process, a C4 hydrocarbon fraction containing about 7 percent butadiene, 25

-per cent normal butenes of which. about onefourth is 1butene andthree-fourths Z-butenes, and 68 per cent normal butane may be passed asa liquid to a fractional distillation column of plates and in twosections operated under a total column pressure of about pounds persquare inch. Sulfur dioxide is introduced to the column in two places,the major part being returned as reflux at a point near the top, withsufficient ,make-up being added along withthe C4 stream to give a totalamount of sulfur dioxide introduced equal to about 10 per cent in excessof that required to form azeotropic mixtures with the normal butane andl-butene introduced, under the conditions existing at the top of thecolumn. Under these conditions a small amount of 2-butene, primarily thetrans-isomer, is included in the overhead product. A sulfur dioxide-richfraction is separated from the overhead product and returned to thecolumn as a liquid reflux, thereby controlling the top temperature andfurnishing sulfur dioxide for the azeotropic distillation.

A kettle product comprising primarily Z-butenes and butadiene is freedfrom traces of sulfur dioxide and passed to a second fractionaldistillation column, containing 120 plates in three sections. Thiscolumn is operated at a pressure of about 75 pounds per square inch, theoverhead fraction contains butadiene of about 98 per cent purity ofwhich a portion is continuously returned as liquid reflux, another beinga product of the process. The kettle product contains only a smallamount of butadiene and comprises primarily 2- butenes.

I claim:

l. In a process for the production of butadiene from normal butane,which comprises dehydrogenating normal butane together with recycled C4hydrocarbons in a single dehydrogenation step under conditions effectingdehydrogenation of normal butane to normal butenes including 1- buteneand Z-butenes and simultaneous dehydrogenation of normal butenes tobutadiene, the improvenient which comprises subjecting eiiiuents of saiddebydrogenation to selective solvent extraction with liquid sulfurdioxide to eiiect a preliminary concentration of butenes and butadiene,'passing `the resulting solution of hydrocarbons and sulfur dioxide to aiirst fractional distillation and removing an overhead fractioncomprising aseotropes of sulfur dioxide with l-butene and normal butane,removing a liquid kettle product consisting essentially of Z-butenes andbutadiene, subjecting said product to a second fractional distillationin the absence of sulfur dioxide, removing therefrom as aA gaseousoverhead product a butadiene concentrate as a product of the process,removing also therefrom a. liquid kettle product substantially free ofbutadiene and comprising essentially 2-butenes and passing same to saiddehydrog'cnation as at least apart oi said recycled C4 hydrocarbons. o t

2. In a process for the production of butadiene from normal butane whichcomprises dehydrozenating normal butane in admixture with recyclednormal butane and butenes under conditions effecting conversion'ofnormal butane to normal butenes including 1butene and 2-butenes andsimultaneous conversion of normal butenes to butadiene, the improvementwhich comprises treating the resulting. eilluent to segregate a fractionconsisting essentially of the C4 hydrocarbon content thereof, extractingsaid C4 hydrocarbon fraction with liquid sulfur dioxide as a selectivesolvent and thereby effecting selective dissolution of the normalbutenes and butadiene content thereof while allowing most of the normalbutane to remain undissolved, recycling said undissolved normal butaneto the dehydrogenating step, passing the rich solvent from saidextracting step to a first fractional distillation zone and therefractionally distilling same in the presence of sulfur dioxide in amountsufiicient to form minimum-boiling azeotropes with all oi the normalbutane and l-butene contained therein but insumcient to form anazeotrope with the maior portion of the Z-butenes contained therein,removing as an overhead all of said azeotropes of sulfur dioxide withnormal butane and 1bu tene, treating the overhead to effect separationthereof into a sulfur dioxide-rich liquid fraction and. a fraction ornormal butane and l-butene. renuxing said distillation zone with atleast a part of said sulfur dioxide-rich liquid fraction. recycling saidfraction of normal butane and 1- butene to said dehydrogenating step,removing from said distillation zone a kettle product consistingessentially oi' 2butenes and butadiene and substantiallyiree oi sulfurdioxide and passing same to a second fractional distillation zone andthere fractionally distilling same in the absence of sulfur dioxide toproduce an overhead product consisting essentially of butadiene as theproduct of the process and a kettle product consisting essentially of2-but'enes, and recycling said 2bu tenes kettle product to saidvdehydrogenating step.

3. The process for the recovery of substantial ly pure butadiene from aCi hydrocarbon fraction containing the same in admixture with l-butene,2-butenes and normal butane which comprises extracting said fractionwith liquid sulfur dioxide as a selective solvent and thereby effectingselective dissolution of the normal butenes and butadiene contentthereof while allowing most of the normal butane to pass throughundissolved, passing 4the resulting rich solvent to a first fractionaldistillation zone and there fractionally distilling same in the presenceof sulfur dioxide in amount suilicient to form minimum-boilingazeotropes with all of the normal butane and l-butene contained thereinbut insuilicient to form an azeotrope with the major portion of the2-butenes contained therein, removing as an overhead all of saidazeotropes of sulfur dioxide with normal butane and l-butene, treatingthe overhead 'to effect separation thereof into a sulfur dioxiderichliquid fraction and a fraction of normal butane and l-butene, re'iluxingsaid distillation zone with at least a part of said sulfur dioxide-richliquid fraction, removing from said distillation zone a kettle productconsisting essentially of 2- butenes and butadiene and substantiallyfree of sulfur dioxide and passing same to a second fractionaldistillation zone and there fractionally distilling same in the absenceof sulfur dioxide to produce an overhead product of substantially purebutadiene and a kettle product consisting essentially of 2-butenes.

FREDERICK E. FREY.

